Microwave device including indium-joined quartz window closing off hermetic chamber

ABSTRACT

A microwave device including an hermetic chamber which is at least partially defined by an electrically conductive wave guide, and by a quartz glass window that is hermetically joined to the wave guide through a sealing medium including indium.

Unite States Patent [191 Hutchins, IV

[ Aug. 6, 1974 MICROWAVE DEVICE INCLUDING INDIUM-JOINED QUARTZ WINDOW CLOSING OFF HERMETIC CHAMBER Thomas B. Hutchins, IV, 310 NW. Brynwood, Portland, Oreg. 97229 Filed: Mar. 1, 1973 Appl. No.: 336,990

Inventor:

US. Cl. 333/98 P Int. Cl. 1101;) 1/08 Field of Search 333/98 P References Cited UNITED STATES PATENTS 11/1951 Malter et a1 333/98 P 7/1954 Curtis 333/98 P 3,212,036 10/1965 Skappaas ..333/98P FOREIGN PATENTS OR APPLICATIONS 775,315 5/1957 Great Britain 333/98 B Primary Examiner-James W. Lawrence Assistant ExaminerWm. H. Punter Attorney, Agent, or FirmKolisch, Hartwell & Dickinson 3 Claims, 6 Drawing Figures 4fl 3% h fi MICROWAVE DEVICE INCLUDING INDIUM-JOINED QUARTZ WINDOW CLOSING OFF HERMETIC CHAMBER BACKGROUND AND SUMMARY OF THE INVENTION This invention pertains to a microwave device, and more particularly, to such a device which includes an hermetic chamber that is at least partially defined by an electrically conductive wave guide, and by a quartz glass window hermetically joined to the wave guide through a ductile sealing medium including indium.

There are various types of microwave devices, such as a microwave oscillator, which must include an hermetic chamber, such as a vacuum chamber, that requires a window allowing the passage of microwave energy between the device and other equipment, such as an adjacent microwave transmission wave guide. The usual oscillator, for example, typically comprises a metallic wave guide portion, suitably sealed at one end, and closed off by such a window at its other end. Various problems have been encountered in the past in the successful construction of such a device, and it is a principal object of the present invention to provide a unique construction which avoids these problems.

One of the key hurdles in the past has been the difficulty of adequately hermetically joining the most satisfactory type of window materials in such a construction. A satisfactory window material is one which neither absorbs significant amounts of microwave energy, nor induces other problems which appreciably affect the efficiency of microwave energy transmission. One of the most desirable materials from this standpoint is quartz glass. However, conventional methods of hermetically joining quartz glass in a construction of the type indicated have not heretofore been successful. A chief difficulty has been that conventional joints, on cooling down from the high temperatures at which they are usually fabricated, are not sufficiently ductile to maintain adequate integrity to withstand, without leakage, high pressure or vacuum hermetic conditions. Another key difficulty has been that known sealing techniques do not result in a good bond to quartz glass. As a practical matter, therefore, quartz glass has not been widely or successfully usable as a window material.

Window materials which have instead been used have included aluminum oxide, and to some extent mica. Aluminum oxide is relatively easy to join hermetically in a device of the type indicated, but is very lossy. In other words, it absorbs significant amounts of microwave energy and thus, appreciably reduces efficiency in a microwave system. Further, aluminum oxide has a high secondary emission coefficient which can result in a window made thereof acting like an electrical short circuit in a system. Mica as a window material must be used in very thin sheets to be effective. And, in thin sheets, mica is extremely fragile and easily damaged. It is ordinarily not capable of sustaining the relatively high pressure or vacuum conditions often requiring in microwave devices. Further, when exposed to pressure or a vacuum, and because of its requisite thinness for effectiveness, it tends to bow out of its plane, which situation further reduces transmission efiiciency.

The present invention overcomes these difiiculties by enabling both the use of quartz glass as a window material, and by providing an effective means for hermetically joining quartz glass in a device as generally described above.

According to a preferred embodiment of the invention, a microwave device is provided including an hermetic chamber (which may be pressurized, or under vacuum)-which chamber is at least partially defined by an electrically conductive wave guide, or the like, and by a quartz glass window that is joined to the wave guide through a sealing medium including ductile indium. As will become apparent below, a good hermetic seal results which allows the use of even extremely high vacuum or other hermetic conditions in the hermetic chamber. Further, the low-loss transmission advantages of quartz glass are obtained.

These and other objects and advantages attained by the invention will become more fully apparent as the disclosure below is read in conjunction with the accompanying drawings.

DESCRIPTION OF DRAWINGS FIG. 1 is a fragmentary side elevationa of microwave apparatus including a device constructed in accordance with the present invention.

FIG. 2 is a fragmentary view, on about the same scale as FIG. 1, taken generally along the line 22 in FIG. 1.

FIG. 3 is an enlarged detail of that portion of FIG. 1 indicated generally by curved line 3-3 in FIG. 1.

FIGS. 4, 5, and 6 are simplified side elevations of three different modifications of the device herein.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the drawings, and referring first to FIGS. 1 and 2, indicated generally at 10 are portions of microwaveequipment including an oscillator 12 coupled to a transmission wave guide 14 through a conventional bolted choke joint 16. It is that portion of oscillator 12 shown in these figures which is constructed in accordance with the present invention.

In other respects, oscillator 12 is conventional. It includes the usual means (not shown) for producing microwave oscillations. The frequency and wavelength of such oscillation might, for example, be 10,000 MHz. and about 3 centimeters respectively. Such oscillations are produced within an evacuated or hermetic chamber 18 within the oscillator--this chamber being bounded and defined by an elongated wave guide 20, a quartz glass window 22 (which closes off the right end of wave guide 20 in FIG. 1), and suitable conventional closing structure adjacent the other end of the wave guide. Oscillator l2 herein is capable of supplying microwave oscillations at a power level of about 1 megawatt, with chamber 18 having therein a vacuum level of better than 10 Torr. When operating, the oscillator is adapted to supply microwave oscillations through window 22 to wave guide 14, in a direction generally to the right in FIG. l-parallel to the axes 12a, 14a of device 12 and wave guide 14.

Wave guide 20 is conventional in construction. It takes the form of a rectangular cross section hollow tube, formed from silver-plated copper. The crossectional outline of tube 20 is partially illustrated in FIG. 2. The wall thickness of this tube herein is about 1 millimeter.

Window 22 has a circular outline, as can be seen in FIG. 2, with a diameter of about 1.5-inches and a thickness of about 0.050-inches. This window is hermetically joined and sealed to wave guide 20 in a manner which will be more fully described shortly.

Wave guide 14 is made of the same material as wave guide 20, and has the same cross-sectional configuration and dimensions. These two wave guides are axially aligned. As was previously mentioned, wave guide 14 is coupled to device 12, and more specifically to wave guide 20, through choke joint 16 which includes the usual quarter-wavelength trap portion 24 secured by means of nut and bolt assemblies 26 to a flange portion 28. The trap and flange portions are made of silverplated copper. Trap portion 24 includes a central rectangular opening 30 which fits snugly about the outside of the right end of wave guide 20 in FIG. 1. The trap portion is anchored to this wave guide as by brazing. Extending in the trap portion radially outwardly from wave guide 20, in a plane flush with the plane containing the right end of the wave guide in FIG. 1, is a surface 32 which aids in supporting window 32. As can be seen in FIG. 2, the circumferential outline of surface 32 is circular and has the same diameter as the window. Formed in the trap portion adjacent the circumference of surface 32 is the usual annular quarter-wavelength trap well 34. This trap well herein is tuned to the frequency of 10,000 MHz., and performs in the usual manner to minimize energy loss in the coupling between device 12 and wave guide 14.

Flange 28 is generally circular, and includes a central rectangular opening 37 which receives the left end of wave guide 14 in FIG. 1. The flange and wave guide 14 are also joined as by brazing.

Considering now FIG. 3 along with FIGS. 1 and 2, it illustrates, in detail, a joint 36 which hermetically joins window 22, wave guide 20, and surface 32. In order to minimize the likelihood of gas loss through this joint, it is, of course, desirable that the joint be as thin as possible. However, in FIG. 3, the joint and its various constituents are shown in greatly thickened or expanded form for the sake of clarity. The overall thickness of joint 36 is about 0.002-inches.

Joint 36 may be thought of as containing five layers, including a layer 38 of platinum, a layer 40 of gold, a layer 42 of a ductile metal (herein indium which is preferred), and a layer 44 of gold. It should be understood that the representations of these layers is schematic only. Because of golds solubility in indium, the interface between the indium and gold layers in the joint would not ordinarily be detectable in a photomicrographic cross section of an actual joint.

Joint 36 may be prepared in the following manner. After suitable cleaning of the confronting portions of wave guide 20, window 22 and surface 32, the confronting portion of window 22 is coated with a metal from the group consisting of platinum, palladium, irridium and rhodium. Such a metal adheres well to quartz glass, and provides a good base for the adherence of remaining constituents in joint 36. A coating of platinum may be prepared by painting on a platinum resinate, such as that contained in Engelhard Companys No. 05-74 Brushing Bright Platinum paint. The win dow, with this painted coating, is then fired in air to a temperature of about 800 C. to decompose the paint and leave a platinum coating. A firmly adhered platinum layer, having a thickness of between about 5 and 10 microinches results. The other types of metal coatings may be prepared in similar manners from EngeL hards No. 761 1 (20 percent palladium), No. 8057 (24 percent irridium), and No. 8826 l0 percent rhodium).

Next, both to the end of wave guide 20 and surface 32, and to the coating of platinum just produced, coatings of gold are produced by painting thereon a resinate product such as Engelhard No. 4813 Liquid Bright Gold paint. The parts are then fired in air to a temperature of about 600 C. Coatings of gold then result, each having a thickness of about 5 to 10 microinches. These gold coatings provide good bonding surfaces for indium, which is the final constituent used in joint 36. Gold bonds well to the silver plating on wave guide 20 and trap portion 24, and hence a preliminary layer of platinum, palladiun, irridium or rhodium is not required.

Next, and in any suitable fashion, a band of indium wire (99.9+% pure) is placed between the gold-coated surfaces just described, with suitable pressure applied to clamp window 22 against the end of wave guide 20 and surface 32. This assembly is then heated in an atmosphere of forming gas, or in a vacuum (better than 10 Torr), to a temperature about 300 C. for about l /2 hours. Forming gas is a mixture by volume of about 10 percent hydrogen and about percent nitrogen. During this process, the indium melts, and spreads in along the interface between the parts through alloying and capillary action. Upon cooling, the indium solidifies, producing, along with the other constituents in the joint, a ductile hermetic joint or seal between the window and the end of wave guide 20 and surface 32. The indium portion of the joint might typically have a thickness of about 0.00l-inches.

A joint thus produced has good integrity and leakage resistance, and has been found to be capable, over long periods of time of withstanding even extremely high vacuum conditions, for example, vacuum levels up to about 10 Torr. As a significant consequence, therefore, a quartz glass window can readily be employed, and its important advantages over other window materials obtained.

FIGS. 4, 5, and 6 illustrate several different modifications, where quartz glass windows are mounted in somewhat different manners in wave guides. For example, in FIG. 4, a microwave deive 46 is shown including a wave guide 48 and a quartz window 50. This device includes an hermetic chamber 46a (to the left of window 50 in FIG. 4). As can be seen, a step or shoulder 47 is provided in the wave guide for supporting window 50. Between the confronting surfaces of window 50 and step 47 is a joint or seal 52, like above-described joint 36. Joint 52 contains five layers including a platinum (or palladium, irridium, or rhodium) layer on the edge of window 50, gold layers on the platinum layer and on step 47, and an indium layer between the gold layers. These may be prepared as described above.

The modification shown in FIG. 5 is similar to that shown in FIG. 4. Here, a microwave device 54 is shown including a wave guide 56 and a quartz glass window 58. As in the case of wave guide 48, the interior of wave guide 56 is stepped at 59 at an angle as shown. A joint 60, like joints 36, 52, joins wave guide 56 and window 58. The hermetic chamber in device 54, shown at 54a, is to the left of window 58 in FIG. 5.

FIG. 6 illustrates a microwave device 62 including a wave guide 64 and a quartz glass window 66. Here, the inside of the wave guide is not stepped. The circumferential edges of window 66 are beveled to afford an adequate joining surface on the window. A joint 68, like joints 36, 52, 60, exists between window 66 and wave guide 64. The hermetic chamber in device 62 is shown to the left of window 66 in FIG. 6 at 62a.

and defining said chamber, and

means including indium hermetically joining said portions and bonding them together as a unit.

2. In a microwave device, the combination compris- It is thus evident that various different specific con- 5 ing 1. A microwave device including an hermetic chamber comprising an electrically conductive wave guide portion partially bounding and defining said chamber, a quartz glass window portion also partially bounding an electrically conductive wave guide portion,

a quartz glass window portion, and

means including indium hermetically joining said portions and bonding them together as a unit,

said portions together at least partially bounding and defining an hermetic chamber in said device.

- 3. A microwave device comprising an electrically conductive metallic wave guide portion,

a quartz glass window portion, and

means including indium hermetically joining said portions and bonding them together as a unit,

said portions together at least partially bounding and defining an hermetic chamber in said device. 

1. A microwave device including an hermetic chamber comprising an electrically conductive wave guide portion partially bounding and defining said chamber, a quartz glass window portion also partially bounding and defining said chamber, and means including indium hermetically joining said portions and bonding them together as a unit.
 2. In a microwave device, the combination comprising an electrically conductive wave guide portion, a quartz glass window portion, and means including indium hermetically joining said portions and bonding them together as a unit, said portions together at least partially bounding and defining an hermetic chamber in said device.
 3. A microwave device comprising an electrically conductive metallic wave guide portion, a quartz glass window portion, and means including indium hermetically joining said portions and bonding them together as a unit, said portions together at least partially bounding and defining an hermetic chamber in said device. 